diff --git a/include/Random123/features/compilerfeatures.h b/include/Random123/features/compilerfeatures.h
index 92b4586..b1935fb 100644
--- a/include/Random123/features/compilerfeatures.h
+++ b/include/Random123/features/compilerfeatures.h
@@ -40,13 +40,42 @@ and idioms that are either not standardized (e.g., asm statments), or for which
 different vendors have their own standards (e.g., SSE intrinsics) or for
 which vendors simply refuse to conform to well-established standards (e.g., <inttypes.h>).
 
-Random123/features/compilerfeatures.h
-conditionally includes a compiler-or-OS-specific Random123/featires/XXXfeatures.h file which
-defines appropriate values for the preprocessor symbols which can be used with
-a specific compiler or OS.  Those symbols will then
-be used by other header files and source files in the Random123
-library (and may be used by applications) to control what actually
-gets presented to the compiler.
+Random123/features/compilerfeatures.h conditionally includes a
+compiler-or-OS-specific Random123/featires/XXXfeatures.h file
+which defines a collection of appropriate values for the
+preprocessor symbols which can be used with a specific compiler
+or OS.  Those symbols will then be used by other header files
+and source files in the Random123 library (and may be used by
+applications) to control what actually gets presented to the compiler.
+
+By default, compilerfeatures.h tries to use predefined compiler
+and architecture symbols (__GNUC__, __CUDACC__, __ICC, __etc) to
+decide which XXXfeatures.h to include.  This can go wrong (e.g.
+compilers other than gcc do defined __GNUC__, pgcc (now nvc)
+started defining __CUDACC_) so a variable R123_USE_AUTOFEATURES
+(which if undefined, defaults to 1) can be set to 0 to turn off
+compiler autodetection and instead, use an R123_XXX symbol to
+specify the features file to use. e.g. define R123_PGCCFEATURES
+to explicitly request the use of pgccfeatures.h.  The following
+compiler features collections are presently available as
+corresponding features files. You can also include the closest
+features file and then override some of its definitions, or just
+not define any of these and define the collection of definitions
+that works on your compiler invocation via -D or the equivalent.
+@verbatim
+         R123_METALFEATURES
+         R123_OPENCLFEATURES
+         R123_ICCFEATURES
+         R123_XLCFEATURES
+         R123_PGCCFEATURES
+         R123_NVCCFEATURES
+         R123_SUNPROFEATURES
+         R123_OPEN64FEATURES
+         R123_CLANGFEATURES
+         R123_FUJITSUFEATURES
+         R123_GCCFEATURES
+         R123_MSVCFEATURES
+@endverbatim
 
 Most of the symbols are boolean valued.  In general, they will
 \b always be defined with value either 1 or 0, so do
@@ -55,13 +84,15 @@ Most of the symbols are boolean valued.  In general, they will
 Library users can override any value by defining the pp-symbol with a compiler option,
 e.g.,
 
-    cc -DR123_USE_MULHILO64_C99 
+    cc -DR123_USE_MULHILO64_C99=1
 
 will use a strictly c99 version of the full-width 64x64->128-bit multiplication
 function, even if it would be disabled by default.
 
 All boolean-valued pre-processor symbols in Random123/features/compilerfeatures.h start with the prefix R123_USE_
 @verbatim
+         AUTOFEATURES
+	 
          AES_NI
          AES_OPENSSL
          SSE4_2
@@ -138,6 +169,20 @@ choose to rely on these:
 
 There are also non-boolean valued symbols:
 
+@verbatim
+R123_METALFEATURES
+R123_OPENCLFEATURES
+R123_ICCFEATURES
+R123_XLCFEATURES
+R123_PGCCFEATURES
+R123_NVCCFEATURES
+R123_SUNPROFEATURES
+R123_OPEN64FEATURES
+R123_CLANGFEATURES
+R123_FUJITSUFEATURES
+R123_GCCFEATURES
+R123_MSVCFEATURES
+
 <ul>
 <li>R123_STATIC_INLINE -
   According to both C99 and GNU99, the 'static inline' declaration allows
@@ -197,33 +242,48 @@ N.B.  When something is added to the list of features, it should be
 added to each of the *features.h files, AND to examples/ut_features.cpp.
 */
 
+/* If R123_AUTOFEATURES is defined to 0, then you must also define
+the symbol for the compiler whose features you want e.g. R123_XLCFEATURES.
+*/
+
+/* By default, use compiler builtin symbols to autodetect which
+XXXfeatures.h to include.  If it goes wrong, define
+R123_USE_AUTOFEATURES to 0 and either define one of the
+R123_*FEATURES that works for you (perhaps overriding selected
+symbols), or write your own and include that before including a
+Random123 header, or define a working collection of symbols on
+the compiler invocation. Apologies in advance! */
+#ifndef R123_USE_AUTOFEATURES
+# define R123_USE_AUTOFEATURES 1
+#endif
+
 /* N.B.  most other compilers (icc, nvcc, open64, llvm) will also define __GNUC__, so order matters. */
-#if defined(__METAL_MACOS__)
+#if defined(R123_METALFEATURES) || (R123_USE_AUTOFEATURES == 1 && defined(__METAL_MACOS__))
 #include "metalfeatures.h"
-#elif defined(__OPENCL_VERSION__) && __OPENCL_VERSION__ > 0
+#elif defined(R123_OPENCLFEATURES) || (R123_USE_AUTOFEATURES == 1 && defined(__OPENCL_VERSION__) && __OPENCL_VERSION__ > 0)
 #include "openclfeatures.h"
-#elif defined(__CUDACC__)
-#include "nvccfeatures.h"
-#elif defined(__ICC)
+#elif defined(R123_ICCFEATURES) || (R123_USE_AUTOFEATURES == 1 && defined(__ICC))
 #include "iccfeatures.h"
-#elif defined(__xlC__) || defined(__ibmxl__)
+#elif defined(R123_XLCFEATURES) || (R123_USE_AUTOFEATURES == 1 && defined(__xlC__) || defined(__ibmxl__))
 #include "xlcfeatures.h"
-#elif defined(__PGI)
+#elif defined(R123_PGCCFEATURES) || (R123_USE_AUTOFEATURES == 1 && defined(__PGI))
 #include "pgccfeatures.h"
-#elif defined(__SUNPRO_C) || defined(__SUNPRO_CC)
+#elif defined(R123_NVCCFEATURES) || (R123_USE_AUTOFEATURES == 1 && defined(__CUDACC__))
+#include "nvccfeatures.h"
+#elif defined(R123_SUNPROFEATURES) || (R123_USE_AUTOFEATURES == 1 && defined(__SUNPRO_C) || defined(__SUNPRO_CC))
 #include "sunprofeatures.h"
-#elif defined(__OPEN64__)
+#elif defined(R123_OPEN64FEATURES) || (R123_USE_AUTOFEATURES == 1 && defined(__OPEN64__))
 #include "open64features.h"
-#elif defined(__clang__) || defined(__bgclang__)
+#elif defined(R123_CLANGFEATURES) || (R123_USE_AUTOFEATURES == 1 && defined(__clang__) || defined(__bgclang__))
 #include "clangfeatures.h"
-#elif defined(__FCC_VERSION) || defined(__FUJITSU)
+#elif defined(R123_FUJITSUFEATURES) || (R123_USE_AUTOFEATURES == 1 && defined(__FCC_VERSION) || defined(__FUJITSU))
 #include "fujitsufeatures.h"
-#elif defined(__GNUC__)
+#elif defined(R123_GCCFEATURES) || (R123_USE_AUTOFEATURES == 1 && defined(__GNUC__))
 #include "gccfeatures.h"
-#elif defined(_MSC_FULL_VER)
+#elif defined(R123_MSVCFEATURES) || (R123_USE_AUTOFEATURES == 1 && defined(_MSC_FULL_VER))
 #include "msvcfeatures.h"
 #else
-#error "Can't identify compiler.  You'll need to add a new xxfeatures.hpp"
+#error "Can't identify compiler.  You'll need to add a new XXXfeatures.hpp"
 { /* maybe an unbalanced brace will terminate the compilation */
 #endif
 
@@ -303,7 +363,7 @@ added to each of the *features.h files, AND to examples/ut_features.cpp.
 #ifndef R123_ULONG_LONG
 #if defined(__cplusplus) && !R123_USE_CXX11_LONG_LONG
 /* C++98 doesn't have long long.  It doesn't have uint64_t either, but
-   we will have typedef'ed uint64_t to something in the xxxfeatures.h.
+   we will have typedef'ed uint64_t to something in the XXXfeatures.h.
    With luck, it won't elicit complaints from -pedantic.  Cross your
    fingers... */
 #define R123_ULONG_LONG uint64_t